(I/O) CommUNIcation between a computer and its users, its storage devices, other computers (via a network) or the outside world. The devices the computer uses to do this are called "peripherals". What actually counts as I/O depends on what level of detail you are considering, e.g. commUNIcation between processors would not be considered I/O when considering a multiprocessor as a single system. Important aspects of I/O are throughput, latency, and whether the commUNIcations is synchronous or asynchronous (using some kind of buffer). (2003-12-04)